Supported metal oxide catalysts are one of the major forms of materials used as heterogeneous catalysts. They are composed of an active material deposited on the surface of a high-surface area support, with the nominal purpose of achieving high dispersion of the active material. However, the support material may contribute to catalysis also, by providing or generating new active sites. With compositions spanning across the Periodic Table, supported metal oxide catalysts are found in industrial chemical processes, commercial applications, and environmental protection, such as automobile catalytic converters, NOx reduction from power plants, petroleum refining, drug manufacture, and petrochemicals processing.
There has been recent interest in surface acid properties of the ZrO2-supported WOx catalyst system due to the low temperature activity of such catalysts for light alkane isomerization. Although less active than sulfated zirconia catalysts, the enhanced stability of ZrO2-supported WOx solid acid catalysts offers an alternative catalyst for practical industrial applications. Such systems are disclosed in U.S. Pat. Nos. 5,401,478; 5,453,556; 5,543,036; 5,552,128; and 5,563,310, the disclosures of which are incorporated herein by reference in their entirety.
Recent investigations into the nature of the tungsten oxide catalytic active sites present in Zrx(OH)4-2x supported WO3 catalysts revealed that Zr-stabilized distorted WO3 nanoparticles (NPs) are responsible for the enhanced catalytic performance of Zrx(OH)4-2x supported WO3 catalysts over model ZrO2 supported WO3 catalysts. The model ZrO2 supported WO3 catalyst consists of a supported tungsten oxide phase containing surface WOx species and crystalline WO3 NPs on a crystalline monoclinic-ZrO2 support.
The preparation methods for catalysts typically involve soaking the support metal oxide in a solution containing the solubilized precursors of the metal oxide to be supported. Drying causes the precursor to adsorb on the surface of the support metal oxide and calcination at high temperatures converts it to a metal oxide. Methods to improve surface area of active catalyst and ensure complete coverage of support materials are required to increase catalytic efficiency and stability.